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is directly connected to the ram, and on account of such intensi-
fication the ram diameter can be as small as we please, merely
strong enough to prevent its bending. The volume in M being
just sufficient to fill the ram cylinder during full stroke, the pistons
F and G fall to the bottom of their cylinders, due not only to
pressure from main, but to a constantly increasing weight of water,
It is this weight, due to water, filling nearly the cylinders D and E,
which, bearing on pistons F and G, so intensifies the pressure in M,
as to support the whole unimmersed ram weight; being clearly a
maximum when the cage is fully raised, and nothing when the
cage is lowered to the bottom. The varying ram weight is, there-
fore, correctly balanced in all positions, and the only load to be
averaged is that of the people. When lowering, water is exhausted
from N, and the descent caused by the weight of the people.

The cord P, passing round a pulley on the working valve Q,
will open the latter to pressure p, or exhaust ey in any position of
cage. If the water in M decrease through leakage, the cage is
lowered to the bottom, and water at N exhausted : then pressure
water being admitted at R, the pistons are forced upward, com-
pelling some water to pass from above to below piston F, through
its packing; at other times R is empty. (See Appendix V.,p. 100,6.)
Intensifiers, or intensifying accumulators, are a means of
transforming small pressure, as from a town main, into a really
useful hydraulic pressure. Recent descriptions will explain the
principle, and good examples will be found at pp. 375 and 836.

Hydraulic Cranes have many advantages over others.
Being worked intermittently, a small pumping engine will store
the power: the.latter, again, being used with considerable rapidity
and saving of time, a consideration when loading vessels at wharves.
The lifting, too, being done without vibration or noise, makes
these cranes of special use in raising foundry boxes and other
like work. The cranes are also very simple.

Fig. 729 shews a cylinder, ram, and pulleys, the essential
apparatus for each motion of a hydraulic crane. Cylinder A has-
a common stuffing box c, packed with hemp, and carries a number
of c fixed' pullies, DX D2 r>s, the ram P supporting an equal
number of * movable' pullies EX E2 E3. To prevent the ram
turning on its axis, the head F slides on guides G G, and the